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Biomechanical evaluation of a novel fenestrated pedicle screw augmented with bone cement in osteoporotic spines.

Study Design. Comparative biomechanical study was conducted in osteoporotic human cadaveric spines. Objective. Determine the influence of the volume of polymethyl methacrylate injected through a fenestrated pedicle screw on the pullout strength and on the ability to safely remove the implant. Summary of Background Data. Pedicle screw fixation in the osteoporotic spine can be improved by the addition of bone cement. Various injection techniques have been used. While improvement has been shown for the pullout strength, the optimal volume of cement to inject has not been previously studied. Methods. Seven osteoporotic spines were instrumented with a standard and a fenestrated pedicle screw augmented with polymethyl methacrylate at each level (T7–L5). Three volumes of bone cement were randomly injected and stratified to the thoracic (0.5 cc, 1.0 cc, and 1.5 cc) and lumbar spine (1.5 cc, 2.0 cc, and 2.5 cc). Axial pullout strength and removal torque of the pedicle screws were quantified. Results. The pullout strength of the fenestrated screw was normalized with respect to its contralateral control. Student paired t tests were conducted and a statistically significant increase was noted for 1.0 cc (186 ± 45%) and 1.5 cc (158 ± 46%) in the thoracic spine and for 1.5 cc (264 ± 193%), 2.0 cc (221 ± 93%), and 2.5 cc (198 ± 42%) in the lumbar spine. There was no significant difference with higher volumes of cement. The median removal torque was 0.34 Nm for the standard and 1.83 Nm for the augmented screws. When the augmented implants were removed, the bone cement sheared completely off at the fenestrations in 15 of the 17 cases. Conclusion. Significant increases in pullout strength can be accomplished by injecting a limited quantity of bone cement through a fenestrated screw while minimizing the risks associated with higher volume. The majority of implants were removed without damaging the vertebra as the bone cement sheared off at the fenestrations.

The incidence and location of corona mortis: a study on 75 cadavers.

We dissected 150 fresh cadaver halves by ilioinguinal exposure, and counted all vessels more than 2 mm in diameter, connecting the obturator system to the external iliac system. The distance between the symphysis pubis and the anastomotic vessels was measured. We found vascular anastomoses between the obturator and external iliac systems in 91 of 150 sides (61%), and anastomotic veins in 78 of 150 exposures (52%). Arterial connections were seen in 29 of the exposures (19%). The mean distance between the anastomotic arteries and the symphysis pubis was 64 (45–90) mm, and 56 (37–80) mm for the communicating veins. There seemed to be no significant difference between genders in the incidence of corona mortis and the distance between communicating vessels and the symphysis pubis.

Biomechanical comparison of a two-level Maverick disc replacement with a hybrid one-level disc replacement and one-level anterior lumbar interbody fusion

BACKGROUND CONTEXT Multilevel lumbar disc disease (MLDD) is a common finding in many patients. Surgical solutions for MLDD include fusion or disc replacement. The hybrid model, combining fusion and disc replacement, is a potential alternative for patients who require surgical intervention at both L5-S1 and L4-L5. The indications for this hybrid model could be posterior element insufficiency, severe facet pathology, calcified ligamentum flavum, and subarticular disease confirming spinal stenosis at L5-S1 level, or previous fusion surgery at L5-S1 and new symptomatic pathology at L4-L5. Biomechanical data of the hybrid model with the Maverick disc and anterior fusion are not available in the literature. PURPOSE To compare the biomechanical properties of a two-level Maverick disc replacement at L4-L5, L5-S1, and a hybrid model consisting of an L4-L5 Maverick disc replacement with an L5-S1 anterior lumbar interbody fusion using multidirectional flexibility test. STUDY DESIGN An in vitro human cadaveric biomechanical study. METHODS Six fresh human cadaveric lumbar specimens (L4-S1) were subjected to unconstrained load in axial torsion (AT), lateral bending (LB), flexion (F), extension (E), and flexion-extension (FE) using multidirectional flexibility test. Four surgical treatments-intact, one-level Maverick at L5-S1, two-level Maverick between L4 and S1, and the hybrid model (anterior fusion at L5-S1 and Maverick at L4-L5) were tested in sequential order. The range of motion of each treatment was calculated. RESULTS The Maverick disc replacement slightly reduced intact motion in AT and LB at both levels. The total FE motion was similar to the intact motion. However, the E motion is significantly increased (approximately 50% higher) and F motion is significantly decreased (30%-50% lower). The anterior fusion using a cage and anterior plate significantly reduced spinal motion compared with the condition (p<.05). No significant differences were found between two-level Maverick disc prosthesis and the hybrid model in terms of all motion types at L4-L5 level (p>.05). CONCLUSION The Maverick disc preserved total motion but altered the motion pattern of the intact condition. This result is similar to unconstrained devices such as Charité. The motion at L4-L5 of the hybrid model is similar to that of two-level Maverick disc replacement. The fusion procedure using an anterior plate significantly reduced intact motion. Clinical studies are recommended to validate the efficacy of the hybrid model.

The Effect on the Pullout Strength by the Timing of Pedicle Screw Insertion After Calcium Phosphate Cement Injection

Study Design Biomechanical Cadaveric Study. Objective To characterize the pullout strength of calcium phosphate cement augmented screws between 0 and 6 minutes after cement injection. Summary of Background Data Earlier studies with calcium phosphate cement on pedicle screws inserted into a metal mold or sawbone have shown that the augmentation strength can be affected by the time between cement injection and screw insertion. However, these studies only compared soft cement to completely hardened cement with extended waiting times. These extended waiting times are impractical in live spinal surgeries. Methods Twenty-four pedicle screws were inserted and pulled out axially from cadaveric bone to make revision models. The 24 screw holes were randomly divided into 4 groups, with each group having 6 holes. For each group, identical pedicle screws were inserted at 0, 2, 4, and 6 minutes after injection with bioresorbable calcium phosphate cement (CPC). After 24 hours, the augmented screws were pulled out axially and their pullout strengths were compared. Results The difference between secondary pullout strength and primary pullout strength increased up to 4 minutes after cement injection but decreased after 6 minutes but without statistical difference among the 4 time settings (P>0.3). Conclusions The augmented screws had similar fixation strength regardless of the time between cement mixture and screw insertion as long as they are inserted within 6 minutes. Augmentation power tends to increase up to 4 minutes after cement injection but decreases after 6 minutes.

Is it safe to back out pedicle screws after augmentation with polymethyl methacrylate or calcium phosphate cement?: A biomechanical study

Study Design Biomechanical cadaveric study. Objective To determine the torque required to remove pedicle screws augmented with polymethyl methacrylate (PMMA) or calcium phosphate cement (CPC); thus, proving the safety of back out of augmented screws in the osteopotoric model, which would be a more dangerous setting than the nonosteoporotic model. Summary of Background Data To our knowledge, no earlier study has characterized the safety of backing out pedicle screw augmented with PMMA or CPC. Methods Pedicle screws were inserted in 24 osteoporotic vertebrae (48 pedicles). The maximal insertion torque and pullout strength of each screw were recorded. After pullout of the pedicle screws, the vertebrae were then randomized into 2 groups of 12 (24 pedicles) each. PMMA was injected into the pedicles in the first group and CPC was injected into the second group after which the pedicle screws were inserted. The pedicle screws were inserted into the pedicle holes augmented with PMMA or CPC, respectively. Finally, all augmented screws were backed out and the maximal removal torque was recorded using a digital torque wrench. Results Throughout the study, no incidence of pedicle or lamina fractures was observed. The average insertion torque was 0.5±0.27 and 0.45±0.29 N·m for groups 1 and 2, respectively (P=0.724). The average pullout strength was 723.1±391.7 and 671.2±383.0 N (P=0.950). After cement augmentation, the average removal torque was 0.77±0.31 and 0.81±0.26 N·m for PMMA and CPC, respectively (P=0.494). Conclusions The results of this study showed that pedicle screws can be easily and safely backed out after augmentation with PMMA or CPC. The result of CPC, however, may only be valid before any bony ingrowth.

Biomechanical evaluation of an expandable meshed bag augmented with pedicle or facet screws for percutaneous lumbar interbody fusion

OBJECTIVE To evaluate the biomechanics of lumbar motion segments instrumented with stand-alone OptiMesh system augmented with posterior fixation using facet or pedicle screws and the efficacy of discectomy and disc distraction. BACKGROUND CONTEXT OptiMesh bone graft containment system has been used for vertebral compression fractures and percutaneous lumbar interbody fusion. The filled mesh bag serves as the interbody device providing structural support to the motion segment being fused. No biomechanical data of this new device are available in the literature. METHODS Twenty-four fresh human cadaveric lumbar motion segments were divided into two groups. In the control group, multidirectional flexibility testing was conducted after an intact condition and standard transforaminal lumbar interbody fusion (TLIF) procedure. In the OptiMesh group, testing was performed following intact, stand-alone OptiMesh procedure, OptiMesh with facet screws (placed using the transfacet approach), and OptiMesh with pedicle screws and rods. Range of motion (ROM) was calculated for each surgical treatment. The lordosis and disc height change of intact and instrumented specimens were measured in the lateral radiographs to evaluate the disc space distraction. In the OptiMesh group, cyclic loading in flexion extension (FE) was applied to measure cage subsidence or collapse (10,000 cycles at 6 Nm). After biomechanical testing, all the specimens were dissected to inspect the discectomy and end plate preparation. The area of discectomy was measured. RESULTS The mean ROM of the intact specimens was 2.7°, 7.4°, and 7.2° in axial torsion (AT), lateral bending (LB), and FE, respectively. There was no difference between the control group and OptiMesh group. The mean ROM of the stand-alone OptiMesh system decreased to 2.4°, 5.1°, and 4.3° in AT, LB, and FE. The ROM decreased to 0.9° in AT, 2.2° in LB, and 0.9° in FE with OptiMesh system and facet screws. On average, OptiMesh system with pedicle screws and rods reduced the ROM to 1.3° in AT, 1.6° in LB, and 1.1° in FE. Compared with the intact condition and stand-alone OptiMesh system, both posterior fixation options had significant statistical difference (p<.001). In AT, ROM of facet screws was lower than that of pedicle screws (p < .05). There was no statistical difference between the facet and pedicle screws in LB and FE (p > .05). The mean volume of bone graft packed into each bag was 8.3 ± 1.5 cc. The average increase of lordosis was 0.6° ± 1.0° after meshed bag was deployed. The average distraction achieved by the OptiMesh system was 1.0 ± 0.6 mm. The average prepared area of discectomy was 42% of the total disc. The disc height change after cyclic loading was 0.2 mm. No subsidence or collapse was noticed. CONCLUSIONS The OptiMesh system offers large volume of bone graft in the disc space with small access portals. The OptiMesh system had similar construct stability to that of standard TLIF procedure when posterior fixation was applied. However, the amount of distraction was limited without additional distraction tools. With the anterior support provided by the expandable meshed bag, facet screws had comparable construct stability to that of pedicle screws. Slightly higher stability was observed in facet screws in AT.

Biomechanical comparison of transpedicular versus extrapedicular vertebroplasty using polymethylmethacrylate.

Study Design An in vitro biomechanical study using osteoporotic cadaveric vertebrae. Objective To compare the biomechanics of transpedicular and extrapedicular approaches in polymethylmethacrylate vertebroplasty in terms of height restoration, strength, and stiffness. Summary Background Data Cement is typically injected through a transpedicular approach in both vertebroplasty and kyphoplasty procedures. Previous biomechanical studies were primarily focused on the transpedicular approach. Extrapedicular approach has been recently developed to provide more symmetric cement filling and has good clinical results. However, no biomechanical data are available to compare these 2 techniques. Methods Twenty-four osteoporotic vertebral bodies were randomly divided into 2 groups for either transpedicular or extrapedicular vertebroplasty. Six lumbar and 6 thoracic vertebrae were used for each group. Each vertebral body was compressed by 25% of its original height and its strength and stiffness were measured. The vertebral bodies were treated with polymethylmethacrylate using either transpedicular or extrapedicular approach. The height restoration was measured before the treated vertebrae were recompressed to determine posttreatment strength and stiffness. Results Both techniques increased vertebral strength by approximately 50% of the intact strength. There was no statistical difference in posttreatment strength between these 2 techniques. However, the transpedicular technique had higher stiffness recovery (70% to 80%) from the intact stiffness than the extrapedicular technique (60%). The extrapedicular approach achieved greater height restoration in thoracic vertebrae. Conclusions Both extrapedicular and transpedicular techniques increased strength but reduced stiffness compared with the intact condition. The extrapedicular technique achieved greater height restoration possibly attributed to its easier access to the fracture site. These biomechanical data provide useful information when selecting an approach for cement injection in vertebroplasty procedures.

Evaluation of injection techniques in the treatment of lateral epicondylitis: a prospective randomized clinical trial

OBJECTIVE We aimed to compare the efficacy of two different injection techniques of local corticosteroid and local anesthetic in the management of lateral epicondylitis. METHODS This prospective study followed 80 consecutive patients who were diagnosed with lateral epicondylitis at our hospital outpatient clinic between 2005 and 2006. Patients were randomly assigned into two equal groups. Group 1 received a single injection of 1 ml betamethasone and 1 ml prilocaine on the lateral epicondyle at the point of maximum tenderness. Group 2 patients received an injection of the same drug mixture. Following the initial injection, the needle tip was redirected and reinserted down the bone approximately 30 to 40 times without emerging from the skin, creating a hematoma. Patients were evaluated with the Turkish version of the Disabilities of the Arm, Shoulder and Hand questionnaire before injection and at the final follow-up. The unpaired t-test and chi-square tests were used to compare results. RESULTS Sixteen patients in Group 1 and 15 patients in Group 2 were lost during follow-up. The average follow-up period of the remaining 49 patients was 21.6 months. There were no significant differences between the two groups with regard to gender, age, follow-up period, symptom duration, involvement side and number of dominant limbs. The Turkish DASH scores of Group 2 were significantly lower than those of Group 1 (p=0.017). CONCLUSION Long-term clinical success in the treatment of lateral epicondylitis depends on the injection method. The peppering technique appears to be more effective than the single injection technique in the long-term.

Should full threaded compression screws be used in adult femoral neck fractures

INTRODUCTION Operative treatment consisting of fracture reduction and fixation, or arthroplasty to permit early patient mobilization, continues to be the treatment of choice for most femoral neck fractures. Options for internal fixation have included a variety of implants; however most recent reports and textbooks cite parallel multiple cancellous screws as the surgical technique of choice. METHODS The study was prospective, randomized and IRB approved. Inclusion criteria included skeletal maturity, closed femoral neck fracture without concomitant fractures or injuries with complete charts and adequate radiographs obtained from the initial injury till the last follow-up. Forty-four patients were enrolled in this study during one-year period at two university centers. 22 were randomized to be treated with full threaded, cannulated compression screws (Acutrak 6/7, ACUMED) (Group 1) and the other 22 with 16mm partial threaded, 6.5mm or 7.3mm cannulated screws (SYNTHES) (Group 2). Three or four screws were used in both groups according to fracture type and surgeons preference. Data evaluated included surgical time, fluoroscopy time, fracture type, radiological outcome, complications and functional status using the Harris Hip Score. RESULTS Both groups were comparable in terms of age and gender. There was not a significant difference in terms of surgical time, follow-up period, fracture type, or fluoroscopy time. There were eight complications in Group 1 and two in Group 2 (P=0.049) Time to union was significantly longer in Group 1 (P=0.001). However, Hip Scores were not significantly different in both groups (P=0.20). CONCLUSION When compared with full threaded compression screws, partial-threaded cannulated screws provides a shorter union time and less complication rate while providing equivalent functional results in adult femoral neck fractures.

A method to calculate relative spinal motion without digitization.

BACKGROUND CONTEXT Euler and projection methods have been used to describe relative spinal motion. In the Eulerian formulation, the exiting method used vector form of Euler angles and only provides an approximation. In the projection method, local coordinate systems constructed with digitization can affect the accuracy of kinematical results. A more consistent data reduction method is desired to calculate relative spinal motion (range of motion) from raw marker data. PURPOSE To develop a new data reduction method to calculate relative spinal motion based on arbitrarily oriented local coordinate systems of individual vertebrae, and to simplify experimental procedures in multidirectional testing of spines. STUDY DESIGN/SETTING The relative spinal motion was determined from raw marker data using transformation matrices. METHODS In the Eulerian formulation, the relative motion of a vertebra to its subjacent level was determined using transformation matrices rather than vector operation on Euler angles. In the projection method, the projection axes were determined by tranforming local coordinate systems. Both approaches can be used to analyze raw marker data. RESULTS The new data reduction method was successfully implemented to analyze the raw data acquired on an intact L1-L2 motion segment. There was little difference between the Euler method and projection methods. CONCLUSIONS In conclusion, an alternative data reduction method in both Euler and projection angles to calculate range of motion for in vitro spine biomechanical studies was presented. The method was validated on a human cadaveric lumbar motion segment under axial torsion, lateral bending, and flexion extension. Because the relative spinal motion does not depend on how local coordinate systems are oriented, the digitization process can be eliminated in most multidirectional flexibility tests. Compared with previous methods, this new method provides more consistent kinematical results and significantly simplifies experimental procedures.